Light emitting device

ABSTRACT

A light emitting device includes a light emitting diode chip, a heat conductive plate mounting thereon the light emitting diode chip, a sub-mount member disposed between said light emitting diode chip and said heat conductive plate, a dielectric substrate stacked on the heat conductive plate and being formed with a through-hole through which the sub-mount member is exposed, an encapsulation member for encapsulation of said light emitting diode chip, and a lens superimposed on the encapsulation member. The sub-mount member is formed around a coupling portion of the light emitting diode chip with a reflective film which reflects a light emitted from a side face of the light emitting diode chip. The sub-mount member is selected to have a thickness such that the reflecting film has its surface spaced away from said heat conductive plate by a greater distance than said dielectric substrate.

TECHNICAL FIELD

The invention relates to a light emitting device using a LED (LightEmitting Diode) chip.

BACKGROUND ART

Japanese Unexamined Patent Application Publication No. 2001-85748(hereinafter referred to as patent document 1) and Japanese UnexaminedPatent Application Publication No. 2001-148514 (hereinafter referred toas patent document 2) propose a light emitting device which comprises aLED chip, a circuit board mounting the LED chip, a metal frame (e.g.made of aluminum) surrounding the LED chip on the surface of the circuitboard, an encapsulation member (e.g. made of transparent resin such asepoxy resin and silicone resin) filled within the frame to encapsulatethe LED chip and bonding wires connected to the LED chip. The framedisclosed in the Patent document 1 and 2 is shaped to have an openingarea which becomes greater as it is spaced away from the circuit boardand is finished to have a mirror interior face which serves as areflector reflecting a light emitted from the LED chip. However, theabove light emitting device is found unsatisfactory in extracting thelight efficiently because of that the light radiated from the side facesof the LED chip is absorbed in the circuit board, or leaked through ajunction between the frame and the circuit board.

DISCLOSURE OF THE INVENTION

In view of the above problem, the present invention has beenaccomplished and has an object of providing a light emitting devicewhich is capable of improving its optical output.

The light emitting device in accordance with the present inventioncomprises the LED chip, a heat conductive plate which is made of a heatconductive material to mount thereon the LED chip, a sub-mount member ofbeing configured to be shaped into a planar plate which is dimensionedto be larger than the LED chip and smaller than the heat conductiveplate, a dielectric substrate stacked on the heat conductive member, anencapsulation member being made of a transparent and elastic material toencapsulate the LED chip, and a lens superposed on the encapsulationmember. The sub-mount member is disposed between the LED chip and theheat conductive plate to relieve a stress applied to the LED chip due toa difference in linear thermal expansion coefficient between the LEDchip and the heat conductive plate. Also, the dielectric substrate isprovided on a surface opposite of the heat conductive plate with a pairof lead patterns for electrical connection respectively with electrodesof the LED chip. Further, the dielectric substrate is formed with athrough-hole through which the sub-mount member is exposed. Thesub-mount member includes a reflection film disposed around a junctionof the LED chip to reflect a light emitted from a side wall of the LEDchip, and is selected to have a thickness such that the reflecting filmhas its surface spaced from the heat conductive plate by a greaterdistance than the dielectric substrate.

Since the light emitting device of the invention is configured toinclude the sub-mount member with a reflection film having such athickness that the surface of the reflecting film is spaced from thehead conductive plate by a greater distance than from the dielectricsubstrate, it is capable of preventing the absorption of the lightradiated from the side wall of the LED chip in a surface or a side wallof the dielectric substrate, thereby improving optical extractionefficiency with an associated improvement of the optical output.

Generally, a color conversion member is deposited on a surface of thedielectric substrate to convert a color of a light radiated from the LEDchip or the metal frame which reflects a light of the LED chip. Byselecting the thickness such that the reflecting film has its surfacespaced from the heat conductive plate by a greater distance than fromthe dielectric substrate, it becomes possible to prevent the light fromleaking through a juncture between the above color conversion member andthe dielectric substrate even if the above color conversion member isdisposed on the surface of the dielectric substrate.

Consequently, it becomes possible to improve the optical extractionefficiency, and reduce color shading too.

Preferably, both of the LED chip and the sub-mount member are eachconfigured to have a square planar shape, and the LED chip is disposedcentrally of the sub-mount member in such a manner that planar sides ofthe LED chip crosses respectively with corresponding ones diagonals ofthe sub-mount member.

In this case, the reflection film can effectively reflect a lightradiated from each side walls of the LED chip towards the sub-mountmember. Preferably, the light emitting device, further, includes theframe provided on a surface of the dielectric substrate to surround thesub-mount member and said the LED chip, and the encapsulation member isdefined by a transparent material filled within the frame. The frame ismolded from a transparent resin.

The frame may be configured to determine the size of the encapsulationmember. Further, in comparison with a conventional case where the frameis made of a metallic material, the frame molded from a transparentmaterial can reduce a difference in linear thermal expansion coefficientbetween the frame and the encapsulation member, and to restrain thegeneration of voids in low temperature condition during a heat cycletest. Moreover, the frame can itself reduce a light reflection loss andtherefore improve the light output efficiency.

Preferably, the LED chip is formed on its one surface with one of theelectrodes and on the other surface with the other electrode. One ofsaid electrodes adjacent to the sub-mount member is connected to onebonding wires through a conductor pattern on the sub-mount member, whilethe other electrode away from the sub-mount member is connected to thebonding wire which extends along one of the diagonals of the LED chip.

In this case, the light radiated from the side wall of the LED has aless chance of being blocked by the bonding wires, whereby it ispossible to reduce the lowering of the optical extraction efficiency dueto the presence of the bonding wires.

Preferably, the light emitting device is configured to further include adome-shaped color conversion member which is disposed on the dielectricsubstrate to cover the lens. The color conversion member is a moldedmember molded from a transparent material mixed with a fluorescentmaterial which is excited by a light emitted from the LED chip andpassing through the encapsulation member to radiate a light having acolor different from that of the LED chip. Further, the color conversionmember is disposed to form an air layer between said color conversionmember and a light emitting face of the lens.

The provision of the color conversion member makes it possible toradiate a color different from that of the LED chip. Also, the colorconversion member is disposed to form an air layer between the colorconversion member and a light emitting face of the lens. When the colorconversion member suffers from an external force, the air layer canrestrain the color conversion member from transmitting a stress to theLED chip through the lens and the encapsulation member. Further, itbecomes possible to reduce an amount of the light being directed andpassing through the lens, a fraction of the light which is radiated fromthe LED chip to be incident upon the color conversion member through thelens and the encapsulation member and is scattered due to thefluorescent particles in the color conversion member. Consequently, anoptical extraction efficiency of the whole device can be improved.Further, the LED chip can be protected from moisture in the externalatmosphere. Since there is no need to make the color conversion memberin an intimate contact to the lens, it becomes possible to reduce a fallof a yield caused by dimensional accuracy or positioning accuracyconcerned with the color conversion member.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional view of a light emitting device inaccordance with an embodiment of the present invention;

FIG. 2 is a partially cutout exploded perspective view the above device;

FIG. 3 is a plan view illustrating a principal part of the above device;

FIG. 4 is a perspective view of a sub-mount employed in the abovedevice;

FIG. 5A is an explanatory View of a principal part of the above device;

FIG. 5B is an explanatory view of a principal part of the above device;

FIG. 6 is a cross-section of another configuration of the above device;and

FIG. 7 is a cross-section of a further configuration of the abovedevice.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be explained in detail withreference to the attached drawings.

As shown in FIGS. 1 and 2, a light emitting device 1 in accordance thepresent embodiment comprises an LED chip 10, a circuit board 20 made ofa thermally conductive material to mount the LED chip 10 thereon, aframe 40 surrounding the LED chip 10 on the surface of the circuit board20, an encapsulation member 50 which is elastic and is made of atranslucent material (transparent resin) filled within the frame 40 toencapsulate the LED chip 10 and bonding wires 14 connected to the LEDchip 10, a lens 60 superimposed on the encapsulation member 50, and adome-shaped color conversion member 70 which is a molded member moldedfrom a transparent material mixed with a fluorescent material anddisposed on the circuit board 20 to cover the lens 60. The lightemitting device 1 of the present embodiment is adapted in use, forexample, as a light source for an illumination appliance, and is mountedon a metal body 100 of the appliance (e.g. made of a metal with a highthermal conductivity such as Al or Cu) through a dielectric layer 90made of, for example, a green sheet. As being mounted on the metal body100 of the apparatus, a thermal resistance from the LED chip 10 to themetal body 100 can becomes less to thereby improve heat-dissipationcapability. Further, since a temperature rise at a junction of the LEDchip can be restricted, an input power can be increased to increase anoutput power. It is noted in this connection that, when the lightemitting devise 1 is used for the illumination appliance, a plurality ofthe light emitting devices 1 may be mounted on the metal body 100 of theappliance in order to obtain an intended output light power, with thelight emitting devices being connected in series or parallel with eachother.

The circuit board 20 includes a metal plate 21 and a dielectricsubstrate 22 made of a glass epoxy board and superimposed on the metalplate 21. The dielectric substrate 22 is provided on its surfaceopposite of the metal plate 21 with a pair of lead patterns forelectrical connection respectively with electrodes (not shown) of theLED chip 10, and is formed with a through-hole 24 through which asub-mount member 30 mentioned hereinafter is exposed. Although, themetal plate 21 is made of Cu in the present embodiment, it may be madeof another metal having a relatively high thermal conductivity, such asAl. Further, in the embodiment, the metal plate 21 is made of athermally conductive material to define itself as a heat-conductiveplate on which the LED chip 10 is mounted. The metal plate 21 is securedto the dielectric substrate 22 by means of an adhesive member 25 made ofan dielectric adhesive sheet film. Instead of the adhesive member 25, itis equally possible to provide a coupling metal layer on the dielectricsubstrate adjacent to the metal plate 21 in order to secure thedielectric substrate 22 to the metal plate 21 by means of the couplingmetal layer.

Each of the lead patterns 23 is realized by a laminate composed of aNi-layer and an Au-layer, and defines an inner lead part 23 a by itsportion located inwardly of the frame 40, and an outer lead part 23 b byits portion not covered by a color transformation member 70. Each oflead patterns 23 is not limited to the laminate of N-layer and Au-layer,and may be realized by a laminate of Cu-layer, Ni-layer, and Ag-layer.

The LED chip 10 is a blue LED chip based on GaN radiating blue light andis configure to have a square planar shape. The LED chip 10 includes anelectrically conductive substrate as an epitaxial substrate, which is an-type SiC substrate having a lattice constant and a crystallinestructure closer to those of GaN than sapphire, and being electricallyconductive. Formed also on the main surface of theelectrically-conductive substrate 11 is a light emitting part 12 whichis made of GaN based semiconductor material and is obtained by anepitaxial growth (e.g, MOVPE process) to have a laminated structure,e.g. double-hetero structure. A cathode electrode (n-type electrode)(not shown) is formed on the back side of the electrically-conductivesubstrate 11 as an electrode on the side of the cathode. An anodeelectrode (p-type electrode) (not shown) is formed on the surface (afrontmost surface of the principal surface of the conductive substrate11) of the light emitting part 12 as an electrode on the side of theanode. In short, the LED chip 10 has the anode electrode on its onesurface, and has the cathode electrode on the opposite surface.

It is noted that, although the present embodiment has the cathodeelectrode and the anode electrode each composed of the laminate ofNi-layer and Au-layer, the cathode electrode as well as the anodeelectrode are not limited to the specific materials, and may be made ofa material (e.g. Al) exhibiting a good ohmic property. Further, thepresent embodiment illustrates that the LED chip 10 is mounted on themetal plate 21 with the light emitting part 12 of the LED chip 10 beingspaced further away from the metal plate 21 than from the electricallyconductive substrate 11. However, it is equally possible to mount theLED chip 10 on the metal plate 21 with the light emitting part 12 beingcloser to the metal plate than the electrically conductive plate 11.Although it is desirable to space the light emitting part 12 apart fromthe metal plate 21 from a viewpoint of optical extraction efficiency,the close disposition of the light emitting part 12 to the metal plate21 does not increase the optical extraction loss because of that theelectrically-conductive substrate 11 and the light emitting part 12 havethe refractive index of the same level in the present embodiment.

The LED chip 10 is mounted on the metal plate 21 through the sub-mountmember 30 within the through-hole 24. The sub-mount member 30 is shapedinto a rectangular plate (a square planar plate in this instance) whichis dimensioned to be larger than the LED chip 10 and smaller than themetal plate 21 and relieves a stress applied to the LED chip 10 due to adifference in linear thermal expansion coefficient between the LED chip10 and the metal plate 21. Further, in addition to relieving theabove-mentioned stress, the sub-mount member 30 has a thermal conductingfunction of conducting the heat generated at the LED chip 10 to themetal plate 21 over an area wider than the size of the chip size of theLED chip 10. The heat generated at the LED chip 10 conducts to the metalplate 21 through the sub-mount member 30 without through the dielectricsubstrate 22.

It is noted in this connection that, although AlN is adopted as amaterial of the sub-mount member 30 because of having both relativelyhigh thermal conductivity and insulating performance, the material ofthe sub-mount member 30 is not limited to AlN, and may be selected tohave the linear thermal expansion coefficient relatively close to thatof electrically-conductive substrate 11 made of 6H—SiC, and relativelyhigh thermal conductivity, e.g. composite SiC, Si, or and the like.

As shown in FIG. 4, the sub-mount member 30 includes a conductivepattern 31 connected to above-mentioned cathode electrode on the surfaceof the LED chip 10, and also includes a reflecting film 32 (e.g.laminate of Ni film and Ag film, Al film, and the like) reflecting alight radiated from the side face of the LED chip 10. In short, thesub-mount member 30 includes the reflection film 32 disposed around ajuncture of the LED chip 10 to reflect the light radiated from the sideface of the LED chip 10. Furthermore, a thickness of the sub-mountmember 30 is selected such that the reflecting film 32 has its surfacespaced from the metal plate 21 (heat conductive plate) by a greaterdistance than from the dielectric substrate 22.

By selecting a thickness of the sub-mount member 30 in above-mentionedmanner in addition to disposing the reflecting film 32 on the sub-mountmember 30, it is capable of preventing the absorption of the lightradiated from the side wall of the LED chip 10 in a surface of thesub-mount member 30 and a side wall of the dielectric substrate 22, andalso the leakage through a juncture between the color conversion member70 and the dielectric substrate 22, thereby improving optical extractionefficiency. Moreover, it is possible to reduce color shading bypreventing the leakage of the light radiated from the side wall of theLED chip 10 through above-mentioned juncture between the colorconversion member 70 and the dielectric substrate 22.

The LED chip 10 has the cathode electrode electrically connected to oneof the lead patterns 23 through the conductive pattern 31 and throughthe bonding wire 14 (e.g. gold thin wire, aluminum thin wire), and hasthe anode electrode electrically connected to the other lead pattern 23through the bonding wire 14.

The LED chip 10 is disposed centrally of the sub-mount member 30 in sucha manner that the planar sides of the LED chip 10 cross withcorresponding diagonals of the sub-mount member 30. In the presentembodiment, the LED chip 10 has its center axis substantially alignedwith that of the sub-mount member 30 along the thickness thereof witheach planar side of the LED chip 10 intersecting the corresponding oneof the diagonals at an angle of about 45°. With such arrangement, it ispossible to reflect the light radiated from each side wall of the LEDchip 10 effectively at the reflecting film 32. The LED chip 10 isdisposed centrally of the sub-mount member 30 in such a manner that theplanar sides of the LED chip 10 cross with corresponding diagonals ofthe sub-mount member 30.

In the present embodiment, the LED chip 10 has its center axissubstantially aligned with that of the sub-mount member 30 along thethickness thereof, while each planar side of the LED chip 10 intersectsthe corresponding one of the diagonals at an angle of about 45°. Withsuch arrangement, it is possible to reflect the light radiated from eachside wall of the LED chip 10 effectively at the reflecting film 32.

As shown in FIG. 3, the light emitting device of the present embodimentis configured such that each of the bonding wires 14 electricallycoupled to the LED chip 10 extends in a direction along a diagonal ofthe LED chip 10 so as to reduce a chance of blocking off the lightradiated from each side of the LED chip 10. Consequently, it is possibleto restrain lowering of the optical extraction efficiency by thepresence of the bonding wire 14.

Although the LED chip 10 and the sub-mount member 30 can be joined by asolder such as SnPb, AuSn, SnAgCu, or a silver paste, they arepreferably joined by use of a lead free solder such as AuSn, SnAgCu.

A silicone resin is used for the encapsulation member 50 as atransparent material. However, the encapsulation member may be made ofan acrylic resin instead of the silicone resin.

The frame 40 is molded from a transparent resin into a cylindricalshape. The frame 40 is provided on the dielectric substrate 22 tosurround the LED chip 10 and the sub-mount member 30. The embodimentillustrates that the frame 40 is made of a silicone resin, namely thetransparent material having a linear thermal expansion coefficientnearly equal to that of the encapsulation member 50. When the acrylicresin is used for the encapsulation member 50 instead of the siliconeresin, it is desirable to mold the frame 40 by use of an acrylic resin.The embodiment denotes that the encapsulation member 50 is defined bythe transparent material which is filled within the frame and heat-curedafter the frame 40 is adhered to the circuit board 20.

With the provision of the frame, the size of the encapsulation member 50can be determined by the frame 40. Furthermore, in comparison with aconventional case where the frame is made of a metallic material, theframe 40 molded from a transparent material can reduce a difference inlinear thermal expansion coefficient between the frame 40 and theencapsulation member 50, thereby restraining the generation of voids inlow temperature condition during a heat cycle test. Moreover, the frame40 can reduce a light reflection loss and therefore improve the lightoutput efficiency.

The lens 60 is configured as a double-convex lens having a convex lightincident surface 60 a opposing the encapsulation 50 and a convex lightemitting surface 60 b. The lens 60 is molded from a silicone resin tohave the same refractive index as the encapsulation 50. The lens 60 isnot limited to the silicone resin mold but may be molded from acrylicresin. The light emitting surface 60 b of the lens is bulged outwardlyso as not to cause the total internal reflection of the light reachingthe light incident surface 60 a at an interface between the lightemitting surface 60 b and the above-mentioned air layer 80. Further, thelens 60 is disposed to have its optical axis aligned with a center lineof the light emitting part 12 extending through the LED chip 10 in athickness direction thereof.

The color conversion member 70 is molded from a mixture of a transparentmaterial, e.g. silicone resin and a particulate yellowish fluorescentmaterial which is excited by a blue light emitted from the LED chip 10and passing through the encapsulation 50 to radiate a broad yellowishwhite light. The light emitted from the side wall of the LED chip 10propagates through the encapsulation 50 and the air layer 80 to reachthe color conversion member 70, exciting the fluorescent material of thecooler conversion member 70 or passing through the color conversionmember 70 without colliding with the fluorescent material. The lightemitting device 1 of the present embodiment can give a white light as acombination of the blue light emitted from the LED chip 10 and the lightemitted from the yellowish fluorescent material.

The color conversion member 70 has its inner surface 70 a shaped inconformity with the light emitting surface 60 b of the lens 60, leavingan uniform tangential distance between the light emitting surface 60 band the inner surface 70 a of the color conversion member 70 over theentire surface of the light emitting surface 60 b. Further, the colorconversion member 70 is shaped to have a uniform thickness along thetangential direction.

The color conversion member 70 is secured at the perimeter of itsopening to the dielectric substrate 22 by means of a bond (not shown)provided by, for example, an adhesive (e.g. silicone resin, epoxyresin), to leave the air layer 80 confined between the color conversionmember 70 and the light emitting surface 60 b of the lens and also theframe 40. The presence of the air layer 80 reduces a possibility of thecontact between the lens 60 and the color conversion member 70 when thelatter is deformed as being subjected to an external force. Therefore, astress developed at the color conversion member 70 due to the externalforce can be prevented from being transmitted to the LED chip 10 as wellas the bonding wires 14, which reduces degradation of luminescentperformance of the LED chip 10 as well as breaking of the bonding wires14, and therefore giving improved reliability. Further, with theprovision of the air layer 80 between the color conversion member 70 andthe lens 60, the LED chip 10 can be protected from moisture in theexternal atmosphere. Furthermore, since there is no need to make thecolor conversion member 70 in an intimate contact to the lens 60 and theframe 40, it is possible to prevent a lowering of yield which would beotherwise caused by dimensional accuracy or positioning accuracyconcerned with the color conversion member 70. Since the colorconversion member 70 is assembled last, it is possible to reduce colorvariance simply by selecting the color conversion member 70 in which themixing ratio of the fluorescent material to the transparent material isadjusted in relation to the wavelength of the light from the LED chip10.

Also, with the provision of the air layer 80 between the colorconversion member 70 and the lens 60, it becomes possible to reduce anamount of the light being diffused back into the lens 60 from the colorconversion member 70, a fraction of the light emitted from the LED chip10 to be incident upon the color conversion member 70 through theencapsulation member 50 and the lens 60 followed by being scattered bythe yellowish fluorescent particles in the color conversion member 70.Consequently, an optical extraction efficiency of the whole device canbe improved.

Explanation is made with reference to FIG. 5A and FIG. 5B in which theoptical axis of the color conversion member 70 is aligned with theoptical axis of the LED chip so that a blue light radiated from the LEDchip 10 is uniformly scattered in every direction from the central pointP of the color conversion member 70 along its optical axis. With regardto the light scattered at point P, the color conversion member 70develops an escape cone ECa having a spread angle 2θa as well as anescape cone ECb having a spread angle 2θb, respectively on inside andoutside of the color conversion member 70. The spread are expressed as2θa=60°, 2θb=98° when the total internal reflection angle φa and φb are40°, as shown in FIG. 5A, and 2θa=76°, 2θb=1340 when the total internalreflection angle φa and φb are 50° as shown in FIG. 5B, where the totalinternal reflection angle φa is defined at the interface between thecolor conversion member 70 and the air layer, while the total internalreflection angle φb is defined at the interface between the colorconversion member 70 and an air, a medium outside of the colorconversion member 70.

The blue light scatted at point P and directed through the escape coneECa on the inside of the color conversion member has a maximum emissionefficiency η which is expressed as η=(1/4 n²)×100 (%), where n is arefractive index of the transparent material forming the colorconversion member 70. Thus, η≈13% when the silicone resin having n=1.4is utilized as mentioned in the above.

In other words, only 13% of the blue light scattered at point P reflectsback to the lens 60 with the provision of the air layer 80 between thecolor conversion member 70 and the lens 60, while as much as about 50%of the blue light reflects without the air layer. Accordingly, theoptical extraction efficiency can be improved and a deterioration of theencapsulation member 50 by blue light can be restrained. It is desirableto use the color conversion member 70 of an increased thickness forreducing the blue light directed through the escape cone ECa.

The transparent material used for the color conversion member 70 is notlimited to the silicone resin, but may include, for example, an acrylicresin, an epoxy resin, glass. Further, the fluorescent material mixed tothe transparent material for the color conversion member 70 is notlimited to the yellowish fluorescent material, and may be replaced witha mixture of a reddish fluorescent material and a greenish fluorescentmaterial which gives a white light. The above embodiment illustrates theuse of the SiC substrate as the electrically conductive substrate 11carrying the LED chip 10 which is the blue LED chip giving a blueluminescence, however, the substrate 11 may be alternatively made of GaNsubstrate. With the use of the SiC- and GaN-substrate, the epitaxialsubstrate has a higher thermal conductivity to reduce the thermalresistance as compared to the dielectric sapphire substrate. The LEDchip 10 may be configured to emit the red or green light, rather thanthe blue light. The material of the light emitting part 12 of the LEDchip 10 is not limited to the GaN-based semiconductor compositematerial, but may include GaAs-based semiconductor composite material,or GaP-based semiconductor composite material.

Furthermore, the electrically-conductive substrate 11 is not limited tothe SiC substrate, but may be selected from GaAs substrate, a GaPsubstrate, and the like in compatible with the material of the lightemitting part 12. As discussed in the above, the light emitting device 1of the present embodiment is configured to include the reflecting film32 on the sub-mount member 30 and also to select the thickness of thesub-mount member such that the surface of the reflecting film 32 isspaced further away from the metal plate (heat conductive plate) 21 thanthe surface of the dielectric substrate 22. With this configuration, thelight emitted from the side wall of the LED chip 10 can be preventedfrom being absorbed in the surface of the sub-mount member 30 or in theside wall of the dielectric substrate, and also from being leakedthrough the juncture between the color conversion member 70 and thedielectric substrate 22, thereby improving the optical outputefficiency. With the improved output efficiency, the light output isimproved. It is noted that, although the present embodiment illustratesthe light emitting device 1 with the frame 40 made of the transparentresin, the frame may be omitted, as shown in FIG. 6.

Further, the light emitting device 1 of the present embodiment mayutilizes a frame 40′ made of a conventional metal instead of the frame40 made of the transparent resin. Also in this case, the sub-mountmember 30 is selected to have a thickness such that the reflecting film32 has its surface spaced from the metal plate 21 (heat conductiveplate) by a greater distance than from the dielectric substrate 22.Thus, it is also possible to make the light emitting device which iscapable of preventing the absorption of the light radiated from the sidewall of the LED chip 10 in a side wall of the dielectric substrate 22and leaking of the light through the juncture between the metal frame40′ and the dielectric substrate 22, thereby improving opticalextraction efficiency with an associated improvement of the opticaloutput.

As discussed in the above, apparently many widely different embodimentsmay be made without departing from the technical concept of the presentinvention, and therefore the present invention should not be limited tothe specific embodiments except as defined in the claims.

1. A light emitting device comprising: a light emitting diode chip; aheat conductive plate which is made of a heat conductive material tomount thereon said light emitting diode chip; a sub-mount member of aplanar plate which is dimensioned to be larger than said light emittingchip and smaller than said heat conductive plate, said sub-mount memberbeing disposed between said light emitting chip and said heat conductiveplate to relieve a stress acting upon said light emitting diode chip dueto a difference in linear thermal expansion coefficient between saidlight emitting diode and said heat conductive plate; a dielectricsubstrate stacked on said heat conductive member, said dielectricsubstrate being provided on a surface opposite of said heat conductiveplate with a pair of lead patterns for electrical connectionrespectively with electrodes of said light emitting diode chip, saiddielectric substrate being formed with a through-hole through which saidsub-mount member is exposed; an encapsulation member being made of atransparent and elastic material to encapsulate said light emittingdiode chip; a lens superimposed on said encapsulation member; andwherein said sub-mount member includes a reflection film disposed arounda juncture of said light emitting diode chip to reflect a light emittedfrom a side face of said light emitting diode chip; and that saidsub-mount member is selected to have a thickness such that saidreflecting film has its surface spaced from said heat conductive plateby a greater distance than said dielectric substrate.
 2. The lightemitting device of claim 1, wherein both of said light emitting diodechip and said sub-mount member are each configured to have a squareplanar shape, said light emitting diode chip being disposed centrally ofsaid sub-mount member in such a manner that planar sides of said lightemitting diode chip crosses respectively with corresponding onesdiagonals of said sub-mount member.
 3. The light emitting device ofclaim 1, further including: a frame provided on a surface of saiddielectric substrate to surround said sub-mount member and said lightemitting diode chip, said encapsulation member being defined by atransparent material filled inside of said frame, and said frame beingmolded from a transparent resin.
 4. The light emitting device of claim1, wherein said light emitting diode chip is formed on its one surfacewith one electrode and on the other surface with another electrode, oneof said electrodes adjacent to said sub-mount member being connected toone bonding wire through a conductor pattern on said sub-mount member,said another electrode away from said sub-mount member being connectedto another bonding wire, said another bonding wire extending along oneof said diagonals of said light emitting diode chip.
 5. The lightemitting device of claim 1, further including a dome-shaped colorconversion member which is disposed on said dielectric substrate tocover said lens, said color conversion member being a molded membermolded from a transparent material mixed with a fluorescent materialwhich is excited by a light emitted from said light emitting diode chipand passing through said encapsulation member to radiate a light havinga color different from that of the light emitting diode chip, said colorconversion member being disposed to form an air layer between said colorconversion member and a light emitting face of said lens.